Krummeich, C. (Corresponding author) ; Universität (Köln) ; Institut für Nuklearchemie (Jülich)

1996
Forschungszentrum Jülich

Report No.: Juel-3263

Abstract: [123I]Iodine is a frequently used radionuclide for analogue tracers in single photon emission tomography (SPET) The goal of this study was to develop new pathways for the direct electrophilic radioiodination ofsmall molecules and the application ofthese methods on the no carrier added (n.c.a.) level in the labelling ofpotential compounds for SPET. The virtually waterinsoluble radioiodination agent Iodo-Gen-", originally developed for radioiodination ofproteins and peptides, was evaluated as an oxidant for the radioiodination of various arenes containing hydroxy or methoxy substituents.. The mechanism of radioiodination in aqueous solution and in the strong organic acid trifluoroacetic acid is discussed. Radioiodination of selected phenols, namely L-a.-methyltyrosine, 4-hydroxyephedrine, metaraminol and N-succinimidyl-3-(4-hydroxyphenyl)propionate (Bolton-Hunter-Reagent) in aqueous solution at both pH 4 and pH 8 give rise to radiochemical yields of 280%. The remarkable pH-dependence of the radiochemical yield with maxima at pH 3-4 and pH 7-8 in aqueous media was investigated. The first maximum at moderate acid conditions is due to the in situ formed N-radioiodoamide, a strong electrophilic iodination reagent. The second maximum at pH 7-8 is a result of the starting deprotonation of the phenol to the phenolate anion At stronger basic conditions the radiochemical yield decreases because more hypoiodite is formed, which, under basic conditions, is a poor iodination reagent

Keyword(s): iodine ; labeled compound ; labeling ; aromatic compound

1. Nuklearchemie (INB-4)